The present invention concerns the supply of a plurality of current levels to an output pad in a device. The invention is useful for reducing such high current switching noise during testing.
When designing devices such as integrated circuits, it is necessary to design output logic circuitry so that sufficient current is available at device outputs to drive the input of other devices. The current needed at an output depends on a number of factors which include the number of devices to be driven by a particular output (i.e., the fan-out of the output), the capacitance of each of the inputs of the devices to be driven, and the desired switching speed.
When output circuitry is designed to generate high current, switching a value on the output often results in high current switching noise. Occurrence of the high current switching noise during testing can result in device failure.
In some cases, devices which are able to function acceptably in applications which require a high current output, may fail testing performed in a typical test environment because of high current switching noise and poor test electronics. In such cases, in the prior art, it was then necessary to either over design the output circuitry of the device so that the device could pass the performance test, or to design custom testers or modify existing testers in order to effectively test the devices.